This invention relates to an improved fusion device capable of heating a plasma to ignition with ohmic heating only and a relatively modest toroidal magnetic field. The great majority of existing and proposed toroidal fusion devices have an axial fusion chamber cross section (i.e., the cross section in a plane which includes the major axis) which is circular or essentially circular. (Examples are the Tokamak Fusion Test Reactor at Princeton University [TFTR Initial Operations by K. M. Young et al. in Plasma Physics and Controlled Fusion, Vol. 26, No. 1A, p. 11, 1984]; The JET Project, Scientific and Technical Developments 1977 and 1978 to 1 June, Report of the European Communities, EUR 6831 en, 1980; International Tokamak Reactor-Phase Two A, Part I [Executive Summary of the IAEA Workshop, 1981-1983] by the INTOR group, Nuclear Fusion, Vol. 23, p. 1513. 1984; Physical Review Letters, Vol. 46, p. 654, 1981 by C. E. Wagner; and Nuclear Fusion, Vol. 20, p. 1255, 1980 by H. A. B. Bodin and A. A. Newton. ) A few toroidal fusion devices have been built with some deviation from a circular cross section. An example is the doublet design as set forth in Ohkawa, U.S. Pat. No. 3,692,626. For the doublet design the maximum vertical dimension of the plasma cross section is approximately 2.5 times the maximum horizontal dimension. (Also see Five Years of Experiments with Non-Circular Plasma in Doublet III, by J. C. Wesley, in ANS Transactions, American Nuclear Society Annual Meeting, New Orleans, June 1984, p. 185. ) For devices with circular or essentially circular plasma cross sections ignition can be obtained only with very high toroidal magnetic field or with intensive auxiliary heating, both of which are extremely expensive.
A Belt Pinch device was constructed by the Max-Planck Institute fur Plasmaphysik in the Federal Republic of Germany which had a plasma cross section with vertical dimension which range from 6 to 11 times the horizontal dimension. This device was heated by shock heating as opposed to ohmic heating which resulted in plasmas with high impurity levels. The highest current achieved was only about 2% of that needed for ignition. That project was abandoned in 1979.